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diff --git a/content/projects/battd.md b/content/projects/battd.md new file mode 100644 index 0000000..3e156cb --- /dev/null +++ b/content/projects/battd.md @@ -0,0 +1,47 @@ +$name battd +$source https://the-tk.com/cgit/battd/ + +battd is a simple battery daemon written for use with a daemontools-style +supervisor. + +$desc + +The daemon `run` script polls the status of a user defined `check` function +every `long_interval` or `short_interval` seconds. The interval is determined by +the status of the `interval` function. On the transition from a successful +`check` exit status to an unsuccessful `check` exit status the `failed` function +is called. These functions and optionally the variables `long_interval` and +`short_interval` need to be provided in a `conf` file located in the same +directory as the script. + +The following `conf` file contains an example configuration which increases the +polling interval from 5 minutes to 30 seconds when the battery level is below 16 +percent or fewer than 20 minutes of battery life remain and puts the machine in +a hybrid sleep once the battery level is below 8 percent or fewer than 10 +minutes of battery life remain. + +```sh +battery=/sys/class/power_supply/BAT0/uevent +interval() { ./battcheck min_time=1200 min_pct=16 "$battery"; } +check() { ./battcheck min_time=600 min_pct=8 "$battery"; } +failed() { zzz -H; } +``` + +Finally, the `battcheck` awk script takes two optional command line variable +assignments for `min_pct` and `min_time` specifying the remaining battery +percentage and remaining battery time in seconds respectively after which the +script will produce an unsuccessful exit code. + +These files should be placed inside a service directory making sure that `run` +and `battcheck` are both executable. The service handles SIGHUP to reload its +configuration at runtime. + +The `battcheck` script is quite versatile and may be useful in other contexts, in +which case it is recommended to install it to `/usr/local/sbin` or another +appropriate location. + +If the script crashes before a success to failure transition of the `check` +function and is re-started after the transition then the script will incorrectly +ignore this transition and not call the `failed` function. This could be fixed +by storing the previous status in on a temporary file system but this was not +done due to the unlikelihood of the event and in order to keep the code simple. |